KH 750 DSP
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Contents
The KH 750 DSP subwoofer .................................................3
Delivery includes ..........................................................3
About this manual..........................................................3
Product overview ..........................................................4
Installing and connecting the KH 750 DSP ....................................6
Preparing the subwoofer ...............................................6
Preparing the room....................................................7
Setting up the subwoofers..............................................7
Positioning the subwoofers.............................................8
Connecting the subwoofer..............................................9
Connecting network cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Connecting/disconnecting the subwoofer to/from the mains power supply ...15
Configuring and using the KH 750 DSP ......................................15
Switching the subwoofer on/o ........................................15
Functionality of the back panel lights ...................................16
AUTO STANDBY switch ................................................17
CONTROL MODE switch ...............................................17
Resetting the KH 750 DSP .............................................17
Firmware update.....................................................17
Calibrating the subwoofer.............................................18
Compensating for larger time of flight (TOF) dierences ..................20
Using the bass management ...........................................20
Remote-controlling the bass management ...............................21
Setting the replay level of the subwoofer................................21
Activating ground lift .................................................22
Cleaning and maintaining the subwoofer.....................................22
Troubleshooting ..........................................................23
Specifications ............................................................24
Pin assignment of the XLR socket ...........................................24
Acoustical measurements and block diagram.................................24
Mechanical drawings ......................................................24
Trademarks ..............................................................24
Technical information & glossary ...........................................25
KH 750 DSP | 2
The KH 750 DSP subwoofer
Thank you for purchasing a Neumann subwoofer. Neumann subwoofers are designed to complement Neumann’s extensive range of monitors. They can be used in music, broadcast, and
post production studios for tracking, mixing, mastering, and home recording. They can be
positioned away from a wall, next to a wall or in a corner and can be mixed freely with other
loudspeakers and subwoofers from the Neumann Studio Monitor Systems range.
The built-in 2.0 / 0.1 Bass Manager can be used in many ways as there are four routing modes
to ensure maximum flexibility when using the subwoofer - see “Uses” below. Fourth order
crossovers and flexible acoustical controls allow for seamless system integration and the bass
management function can be remotely controlled.
State-of-the-art circuitry design and the specially developed long excursion bass driver have
been used to ensure the most accurate sound reproduction possible. Neumann products are
designed for longevity so we hope you enjoy many happy years of using this product.
Uses
• Bass extension for loudspeakers
• Increasing the maximum SPL of loudspeakers
• Decreasing harmonic and intermodulation distortion of loudspeakers
• Reproducing the LFE channel
• Reproducing the “Sub” signal of a bass managed multichannel source
• Working as an extension for KH 810, KH 870 and KH 805 subwoofer systems
• Making a Plane Wave Bass Array™ system
• Improving the modal behaviour of the room due to optimal placement of the subwoofer in
the room.
Delivery includes
1 KH 750 DSP subwoofer
4 Rubber feet
1 Quick guide
1 Safety guide
Delivery also includes European, UK or US mains cables
About this manual
This operating manual describes the physical setup and autonomous operation of the
KH 750 DSP. For information about using the KH 750 DSP in a network please refer to the very
helpful Neumann.Control software.
Some of the advantages of exploring Neumann.Control are:
• More extensive acoustical controls for more accurate audio reproduction
• System-wide control such as volume control, soloing and muting
• Rapid system re-purposing
When released, to download the app for Android or iOS tablets go to the Google Play Store or
Apple App Store and search for “Neumann.Control”.
When released, to download the software for PC or Mac go to www.neumann.com and find the
download section in the KH 750 DSP product page.
The current operating manual as well as the quick guide and the safety guide can also be
downloaded from the “Downloads” area on the product page at www.neumann.com.
Note that imperial dimensions are approximate.
KH 750 DSP | 3
Product overview
1
2
1 Neumann logo
2 Metal grille
KH 750 DSP | 4
G
F
E
D
C
B
A
0
H
IJ
3
3 MAINS POWER switch
4 IEC mains socket with protective ground contact
5 LOW CUT potentiometer
6 INPUT GROUND LIFT switch
7 ETHERNET CONTROL NETWORK socket
8 XLR3-M sockets
ANALOG OUTPUT | LEFT/A
ANALOG OUTPUT | RIGHT/B
9 XLR3-F sockets
ANALOG INPUT | LEFT/A
ANALOG INPUT | RIGHT/B
0 BNC sockets
DIGITAL | AES3 INPUT
DIGITAL | AES3 OUTPUT
4
89 67 5
A SUBWOOFER GAIN | OUTPUT LEVEL switch
B SUBWOOFER GAIN | INPUT GAIN potentiometer
C SUBWOOFER PHASE switch
D SUBWOOFER PHASE switch
E BASS MANAGEMENT switch
F BASS MANAGEMENT LED
• green = active
G AUTO STANDBY switch
H POWER ON LED
• green = on
• red = protection active
• amber = indication
I CONTROL MODE switch
J CHANNEL B INPUT MODE switch
KH 750 DSP | 5
Installing and connecting the KH 750 DSP
Have the product installed and connected by a specialist. Due to his/her technical training,
know-how and experience as well as knowledge of relevant provisions, regulations and standards, the specialist must be able to assess assigned tasks, recognize potential hazards and
ensure appropriate safety measures. The following safety and mounting instructions are
addressed to this specialist.
CAUTION
Danger of injury and material damage due to tipping/dropping of the product!
If improperly mounted, the product and/or the mounting hardware (e.g. rack) can tip over
or drop down.
X
Always have the product mounted by a qualified specialist according to local, national
and international regulations and standards.
X
Use the mounting systems recommended by Neumann and always provide sucient additional protection against tipping or dropping by means of safety wires.
CAUTION
Damage to the product due to overheating!
If air cannot circulate properly around the rear of the subwoofer, the power amplifiers may
overheat leading to premature activation of the thermal protection system which limits the
maximum output level of the subwoofer. In rare cases, damage to the product may also
occur.
X
The whole of the back panel should have a free flow of air to ensure good cooling.
X
When installing the product into tight spaces such as wall recesses, maintain an air gap
of at least 2" (5 cm) around the subwoofer’s backplate to ensure a free air flow.
For information on installation, please refer to the supplied “Getting Started Quickly”
supplement. This will help you set up the subwoofers and loudspeakers in a way that
will give you the best acoustic performance from the system. For further information on
setting up subwoofers and loudspeakers, please refer to the “Questions & Answers” section at www.neumann.com.
Preparing the subwoofer
CAUTION
Risk of staining surfaces!
Some surfaces treated with varnish, polish or synthetics may suer from stains when they
come into contact with other synthetics. Despite a thorough testing of the synthetics used
by us, we cannot rule out the possibility of staining.
X
Do not place the KH 750 DSP on delicate surfaces.
To place the subwoofer on a flat surface:
X
Attach the supplied self-adhesive feet to the bottom of the cabinet, about 2-3 cm (1") from
the edges.
This reduces the risk of scratching the surface and acoustically isolates the subwoofer from
the surface.
X
Alternatively, the feet can be stuck onto the side of the cabinet if that helps with mounting
the product in the room.
If you want to hide the subwoofer:
X
Use a thin open weave cloth. To provide visual cover, you can use two layers of the cloth.
KH 750 DSP | 6
Preparing the room
X
Arrange all acoustically relevant surfaces and objects symmetrically on either side of the
listening axis of the room (left/right).
X
Minimize the sound that is reflected back to the listening position by using angled surfaces
and/or acoustical treatment.
X
The subwoofer can delivery very low frequencies at high levels which can lead to objects and
parts of the room structure to rattle. Ensure that rattling and resonating surfaces are avoided.
This product has been optimized for use in recording studios. In order to avoid aecting
the quality of reproduction, make sure that the product is used in an EMC environment.
Setting up the subwoofers
Choosing the type of setup
The driver is located on the front panel of the subwoofer, allowing the subwoofer to be either
set up in a room or flush mounted into a wall recess.
Flush mounting the subwoofer into a wall recess or placing it directly against the wall oers
the following advantages:
• A solid wall boosts the level of the subwoofer in the room which can be compensated by
reducing the output level of the subwoofer. This also reduces distortion resulting in a cleaner
sound reproduction.
• Reflections from the wall behind the subwoofer are eliminated so that the frequency
response becomes smoother.
• The subwoofer does not occupy space in the room when flush mounted.
If you want to flush mount the subwoofer into a wall recess:
X
Have the wall constructed by an experienced acoustical engineer. At least the following points
should be observed:
• The wall should be solid (stone, brick, concrete, several layers of gypsum or MDF).
• Ensure a free air flow around the rear of the subwoofer.
Using one or several subwoofers
X
Use ...
one subwoofer several subwoofers
... if your room does not oer sucient
space for several subwoofers.
To reduce low-frequency distortion, the uncalibrated output level of your subwoofer
should always be higher than the output level of your loudspeakers. We recommend
using arrays with several subwoofers, in which case the uncalibrated maximum output
level of the subwoofer array should also be higher than the maximum output level of all
the loudspeakers in the system. The subwoofers can then be calibrated to a lower output
level resulting in lower distortion and correspondingly cleaner low-frequency
reproduction.
For information on building a balanced system, please refer to the “Product Selection
Guide” at www.neumann.com.
The Neumann.Control software must be used to set up multiple subwoofer systems.
... if you need to move left and right
along the mixing console, or if there are
several listening positions along a large
format mixing console.
... if you require a higher output power
or less distortion with the same output
power.
... to suppress lateral modes or cross
modes in the room by means of a Plane
Wave Bass Array (PWBA™).
... if many smaller cabinets are easier to
position than one large cabinet.
KH 750 DSP | 7
Positioning the subwoofers
Regardless of whether you are setting up one or several subwoofers:
X
d
wall
Always ensure that the distance d
woofer’s front is less than 0.8 m.
If you are setting up one subwoofer:
X
Position the subwoofer against the front wall, left or right of the middle of the front wall
ideally at 1/4 or 3/4 of the room width.
X
Do not place the subwoofer at the side wall or rear wall of the room as sometimes proposed
for domestic applications.
If you are setting up several subwoofers as a Plane Wave Bass Array™ (PWBA™):
X
Use two to four subwoofers for smaller rooms and three to four subwoofers for larger rooms.
X
Set up the subwoofers along the front wall within half a wavelength of the upper cut o frequency of each other. The maximum spacing of the subwoofer cabinets is determined by the
setting of the routing mode or crossover frequency (see page 21):
Setting Max. spacing of the subwoofer cabinets
RIGHT approx. 2 m (6'6")
EXTERNAL BASS MANAGEMENT depends on crossover frequency setting in the
LFE-MODE 1 approx. 1.4 m (4'6")
LFE-MODE 2 approx. 2 m (6'6")
If you observe the stated spacing, the subwoofers form a cylindrical source and generate
a plane wave down the room, a so-called Plane Wave Bass Array™ (PWBA™). The PWBA™
reduces stationary waves between the side walls, improves the bass reproduction and
suppresses lateral room resonances.
between the wall behind the subwoofer and the sub-
wall
source equipment, for 80 Hz approx. 2 m (6'6")
Utilizing the
acoustical gain
You can correct excessive low frequency energy in the room using the potentiometer
SUBWOOFER GAIN| INPUT GAIN B and the switch SUBWOOFER GAIN | OUTPUT LEVEL A
(cf. page26).
If you set up several subwoofers, you can utilize their mutual coupling to achieve an acoustical
gain. The following acoustical gains are possible:
Number of subwoofers Acoustical gain
1 0.0 dB
2 6.0 dB
3 9.5 dB
4 12.0 dB
KH 750 DSP | 8
Positioning and orienting subwoofers and loudspeakers
Subwoofers are omni-directional in their typical pass band as the generated wavelength is
long compared to the surface producing the sound, therefore it does not matter in which direction the subwoofer is oriented when placed in the listening environment.
For your loudspeakers, however, an accurate positioning and orientation is vital.
X
Position your loudspeakers as follows:
System Position and orientation
2.0 (stereo) ±30°
5.1 ITU-R BS.775-1:
0°, ±30°, ±110° (±10°)
(center, front left/right, surround left/right)
ANSI/SMPTE 202M:
0°, ±22.5°, arrays to the surround left and to the surround right,
plus optional subwoofer(s)
6.1 as 5.1 systems plus 180° (back center)
7.1 0°, ±30°, ±90°, ±150°
(center, front left/right, side left/right, back left/right)
For detailed information on the positioning and orientation of your loudspeakers, please refer
to the operating manuals of the loudspeakers.
If your subwoofers cannot be placed at the same distance from the listening position as the
loudspeakers, time-of-flight dierences will occur.
X
Avoid distance dierences of > 2m (6'6").
X
Compensate for time-of-flight dierences as described in the chapter “Calibrating the phase”
on page 19.
Connecting the subwoofer
Signal
(source connector)
Analog (RCA) low up to 10 m
Analog (XLR) low up to 100 m
AES3 (BNC) 75 Ω up to 100 m
AES3 (XLR) 110 Ω up to 100 m
S/P-DIF (RCA) 75 Ω up to 10 m
The default signal selection is analog. If a valid digital signal is connected to the digital
input this digital signal is automatically selected. In Neumann.Control it is possible to select
between automatic signal switching, analog or digital.
Note: If the source equipment is digital, we recommend using digital connections from the
source to the subwoofer as this avoids additional unnecessary signal conversions.
Source
impedance
Cable length Subwoofer connection method
via an adapter (RCA-XLR)
(30')
(300')
(300')
(300')
(30')
to the ANALOG INPUT socket (XLR)
9 (see below)
directly to the ANALOG INPUT
socket (XLR) 9 (see below)
directly to the DIGITAL INPUT
socket (BNC)0 (see page 10)
via an impedance converter and an
adapter (XLR-BNC) to the DIGITAL
INPUT socket (BNC)0 (see page
10)
via an adapter (RCA-BNC) to the
DIGITAL INPUT socket (BNC)0 (see
page 10)
KH 750 DSP | 9
Output (RCA)
Input (XLR-M)
110
cable
AES3 on XLR to AES3 on BNC Connections
75
cable
110
57 mW
54.9
112 mW
187
26 mW
56.2
1.2 mW
Use E96 1% resistors
Source
(XLR-F)
Subwoofer
(BNC)
Connecting
unbalanced
cables
Connecting analog signals to the KH 750 DSP
X
Use balanced XLR cables to connect the corresponding sockets ANALOG INPUT 9 of the
KH 750 DSP to the audio source.
X
Use an XLR adapter (not supplied) to connect unbalanced cables (e.g. RCA cables).
following wiring if you want to make your own XLR adapter:
Wiring Pin Signal
1 Audio ground
2 Signal +
3 Signal -
The level delivered by devices with RCA outputs (-10 dBV) is usually less than the studio
level (+4 dBu):
X
If necessary, use active unbalanced-to-balanced converters in order to be able to connect
devices with unbalanced signals.
X
We do not recommend passive unbalanced to balanced converters using transformers. They
usually limit low frequency levels and increase high frequency distortion.
Use the
Connecting
AES cables
Connecting digital signals to the KH 750 DSP
X
Connect the digital AES3 or S/P-DIF-output signal of your audio source to the DIGITAL INPUT
socket 0 of the respective KH 750 DSP. See picture below.
The KH 750 DSP subwoofer only supports non-encoded AES3 and S/P-DIF signals. Encoded signals such as MP3, DTS or Dolby Digital are not supported.
Only one cable is needed for uncompressed AES3 and S/P-DIF digital signals
(single-wire mode). They contain two audio channels: “subframe A” and “subframe B”. Usually, the audio channels are:
Subframe A Subframe B
Left Right
Center LFE
Surround left Surround right
Back left Back right
A clock input is not required because subwoofers are not audio sources and the
converters are clocked to a very stable internally generated clock source.
X
Use a Neutrik NADITBNC-F impedance and level converter (not supplied) for XLR to BNC
conversions of AES3-signals. This method brings impedance matching, level matching and
source-receiver isolation. The Neutrik NADITBNC-F converter is guaranteed to work up to
48kHz. Only one converter is needed per digital signal cable.
X
Use the following wiring if you want to make your own converter:
CAUTION
Damage to the product due to high AES3 signal levels!
AES3 signal levels in XLR cables are much too high for the
(BNC)0. If you connect such signals without reducing the signals’ level, damage to the
product will occur.
X
Always make sure that your converter is able to match impedance and level.
DIGITAL INPUT socket
Wiring Pin Signal
1 Shield
2 Signal +
3 Signal -
This method brings impedance matching and level matching, but no source-receiver isolation.
Use a resistor network to passively attenuate the XLR signal from 3.1 V down to 0.42V and
change the impedance from 110 to 75 .
KH 750 DSP | 10
Connecting loudspeakers to the subwoofer
Source Signal: Analog
Subwoofer-loudspeaker connections: Analog
Source Signal: Digital
Subwoofer-loudspeaker connections: Analog
Source Signal: Analog
Subwoofer-loudspeaker connections: Digital
Note: Set the left loudspeaker input signal
select to Digital A and the right loudspeaker
input signal select to digital B.
Source Signal: Digital
Subwoofer-loudspeaker connections: Digital
Note: Set the left loudspeaker input signal
select to Digital A and the right loudspeaker
input signal select to digital B.
For a simplified representation, the following connection examples show loudspeakers in combination with the KH 750 DSP subwoofer. Each of the examples only shows one possible combination of loudspeakers and subwoofers. For information on building a balanced system,
please refer to the “Product Selection Guide” at www.neumann.com.
Either use balanced XLR cables to connect the corresponding ANALOG OUTPUT 8 sockets of
the subwoofer to the analog input sockets of the loudspeakers or use the DIGITAL OUTPUT 0
socket for loudspeakers with digital inputs.
Stereo systems
Full range stereo (bass managed): two loudspeakers and one subwoofer
X
Find the correct cabling diagram below depending on your source signal type (analog or
digital) and the subwoofer/loudspeaker interconnection signal type (analog or digital).
X
Set the CHANNEL B INPUT MODE switch J to STEREO.
ANALOG INPUT LEFT/A
9 8
ANALOG OUTPUT LEFT/A
Sub
L
R
ANALOG INPUT RIGHT/B ANALOG OUTPUT RIGHT/B
ANALOG IN
ANALOG IN
0 8
DIGITAL AES3 INPUT
ANALOG OUTPUT LEFT/A
Sub
L/R
89
ANALOG IN
ANALOG IN
ANALOG OUTPUT RIGHT/B
8
ANALOG INPUT LEFT/A
L
R
ANALOG INPUT RIGHT/B
9 0 0
Sub
9
DIGITAL AES3 OUTPUT
DIGITAL IN
DIGITAL OUT
DIGITAL IN
DIGITAL AES3 INPUT
Sub
L/R
DIGITAL AES3 OUTPUT
DIGITAL IN
DIGITAL OUT
DIGITAL IN
KH 750 DSP | 11
0
Full range stereo (bass extension): two loudspeakers and two subwoofers
Source Signal: Analog
Subwoofer-loudspeaker connections: Analog
Source Signal: Digital
Subwoofer-loudspeaker connections: Analog
Source Signal: Analog
Subwoofer-loudspeaker connections: Digital
Source Signal: Digital
Subwoofer-loudspeaker connections: Digital
Note: Set the left loudspeaker input signal
select to Digital A and the right loudspeaker
input signal select to digital B.
Note: Set the left loudspeaker input signal
select to Digital A and the right loudspeaker
input signal select to digital B.
X
Find the correct cabling diagram below depending on your source signal type (analog or
digital) and the subwoofer/loudspeaker interconnection signal type (analog or digital).
X
Set the CHANNEL B INPUT MODE switch J to STEREO.
ANALOG INPUT LEFT/A
9
ANALOG OUTPUT LEFT/A
Sub L
L
R
ANALOG IN
ANALOG IN
Sub R
ANALOG INPUT RIGHT/B ANALOG OUTPUT RIGHT/B
ANALOG INPUT LEFT/A
9
9
DIGITAL AES3 OUTPUT
Sub L
L
R
DIGITAL IN
DIGITAL IN
Sub R
ANALOG INPUT RIGHT/B DIGITAL AES3 OUTPUT
9
8
DIGITAL AES3 INPUT
ANALOG OUTPUT LEFT/A
0
8
Sub L
L
R
ANALOG IN
ANALOG IN
Sub R
8
0
DIGITAL AES3 INPUT ANALOG OUTPUT RIGHT/B
DIGITAL AES3 INPUT
0
0
DIGITAL AES3 OUTPUT
8
0
Sub L
L
R
DIGITAL IN
DIGITAL IN
Sub R
0
DIGITAL AES3 INPUT DIGITAL AES3 OUTPUT
0
0
KH 750 DSP | 12
Source Signal: Analog
Subwoofer-loudspeaker connections: Analog
Source Signal: Digital
Subwoofer-loudspeaker connections: Analog
Source Signal: Analog
Subwoofer-loudspeaker connections: Digital
Source Signal: Digital
Subwoofer-loudspeaker connections: Digital
Note: Set the center loudspeaker input signal
select to Digital A
Note: Set the center loudspeaker input signal
select to Digital A
Multichannel
systems
Discrete multichannel systems (professional applications)
In multichannel systems, stereo pairs of loudspeakers (L/R, Ls/Rs, etc.) can be connected to
subwoofers as shown above.
X
For the Center and Sub/LFE channels, find the correct cabling diagram below depending on
your source signal type (analog or digital) and the subwoofer/loudspeaker interconnection
signal type (analog or digital).
X
The Center channel must be connected to the analog A input or be located on the digital
A channel. The Sub/LFE channel must be connected to the analog B input or be located on
the digital B channel.
X
Depending on how you wish to handle the Sub/LFE channel, set the CHANNEL B INPUT
MODE switch J to EXTERNAL BASS MANAGEMENT, LFE-MODE 1 or LFE-MODE 2.
• EXTERNAL BASS MANAGEMENT replays the “Sub” channel full range through the subwoofer (preferred setting for already encoded signals or a mixing console with bass
management enabled). In the source equipment, set the loudspeakers to “Small” and
the crossover frequency to 80 Hz.
• LFE-MODE 1 replays the LFE channel up to 120 Hz through the subwoofer (preferred setting for movie mixes, pre-encoded mixes).
• LFE-MODE 2 replays the LFE channel up to 80 Hz through the subwoofer and above 80
Hz through the connected center loudspeaker, thereby giving full range monitoring for
the LFE channel (preferred setting for music mixes).
ANALOG INPUT LEFT/A
C
Sub/LFE
ANALOG INPUT RIGHT/B
ANALOG INPUT LEFT/A
C
Sub/LFE
9 8
ANALOG OUTPUT LEFT/A
Sub
ANALOG IN ANALOG IN
9
9 0
DIGITAL AES3 OUTPUT
Sub
DIGITAL IN DIGITAL IN
DIGITAL AES3 INPUT
C
Sub/LFE
DIGITAL AES3 INPUT
C
Sub/LFE
Sub
Sub
ANALOG OUTPUT LEFT/A
DIGITAL AES3 OUTPUT
80
00
ANALOG INPUT RIGHT/B
9
KH 750 DSP | 13
Bass managed multichannel systems (domestic applications)
Source Signal: Analog
Source Signal: Digital
X
In multichannel systems where there is a bass manager preceding the monitoring system
(for example in surround sound processors), connect the loudspeakers and subwoofer(s)
directly to the source equipment (analog or digital). The “Sub” signal should be connected
to the analog B input or be located on the digital B channel.
X
Set the CHANNEL B INPUT MODE switch J to EXTERNAL BASS MANAGEMENT.
X
In the surround sound processor, set the loudspeakers to “Small” and the crossover frequency to 80 Hz.
Sub
ANALOG INPUT
RIGHT/B
9 0
Sub
Sub
DIGITAL AES3
INPUT (B channel)
Sub
Connecting network cables
To use the extended functionality oered by the Neumann.Control software, the subwoofer
must be connected to a standard network switch using a user supplied standard Ethernet cable
(Cat 5 or better). The maximum length of the cable is 100 m.
Refer to the Neumann.Control software help for information about how to use subwoofers in a
network.
RJ45 RJ45 RJ45RJ45
Network Switch
KH 750 DSP | 14
Connecting/disconnecting the subwoofer to/from the
3
mains power supply
To connect the KH 750 DSP to the mains power supply:
X
Make sure that the switch MAINS POWER 3 is set to “OFF”.
X
Connect the IEC connector of the supplied mains cable to the IEC mains socket 4.
4
Power Source
X
Connect the mains plug of the mains cable to a suitable wall socket.
To disconnect the KH 750 DSP from the mains power supply:
X
Set the switch MAINS POWER 3 to “OFF”.
X
Pull the mains plug out of the wall socket.
Configuring and using the KH 750 DSP
On/o switching
using the switch
MAINS POWER 5
Switching the subwoofer on/o
You can switch the KH 750 DSP on and o using the switch MAINS POWER 3.
X
Set the switch MAINS POWER 3 to:
• “ON” to switch the subwoofer on. The POWER ON LEDH lights up red for 5 seconds, during which the subwoofer is muted (see below). The POWER ON LEDH then lights up
green.
• “OFF” to switch the subwoofer o. The POWER ON LEDH lights up red and goes o after
a few seconds. The subwoofer mutes immediately when it is switched o.
There is a five second delay before sound can be heard from the KH 750 DSP and the
loudspeakers connected to the outputs in order to avoid noises (pops) from preceding
equipment switched on at the same time. Conversely, switching o the subwoofer
immediately mutes the audio.
KH 750 DSP | 15
Functionality of the back panel lights
Action Indication
Firmware activities
Subwoofer is booting up Power LED solid red
Subwoofer boot up error Power LED flashing red
Subwoofer firmware is being updated Power LED solid amber
Subwoofer resetting to factory default settings Power LED flashing red
Everyday operation
Operating normally Power LED solid green
Subwoofer in active system is solo’ed in
Neumann.Control
Subwoofer system output level is muted
(GUI button on Operate page)
Subwoofer system output level is dimmed
(GUI button on Operate page)
Bass management disabled Bass management LED o
Bass management active Bass management LED green
Protection
Protection system is activated (takes priority over
other indications)
Power LED solid green
Power LED solid red
Power LED solid green
Power LED red
Neumann.Control Alignment
Setup: Identify the Subwoofer Power LED flashing amber
Guided Alignment: Subwoofer is selected Power LED flashing amber
Manual Alignment: Subwoofer is selected Power LED flashing amber
KH 750 DSP | 16
AUTO STANDBY switch
If the AUTO STANDBY switch G has been set to ON, the KH 750 DSP will switch to standby after
90 minutes without an input signal.
Standby means that the network interface, signal processing circuitry and power amplifiers
are all powered down. Standby mode is automatically deactivated when a suciently large
audio signal is detected at the input. The time taken to resume normal operation and hear
sound is 5 seconds. It is possible to change the time and standby signal level before standby
mode is activated using the Neumann.Control software.
Standby can be disabled by moving the AUTO STANDBY switch G to OFF.
CONTROL MODE switch
If the CONTROL MODE switch I has been set to LOCAL, the KH 750 DSP will not react to network commands from the Neumann.Control software. Control of the subwoofer will be from the
backplate only.
If the CONTROL MODE switch I has been set to NETWORK, the KH 750 DSP will react to network commands from the Neumann.Control software. All backplate controls marked with “*”
will be ignored.
If the CONTROL MODE switch I is set to NETWORK but there is no network connection and
active Neumann.Control software, the last used network configuration will be used. If the
Neumann.Control software has not been connected before, the default settings will be used.
If you have configured any settings via the Neumann.Control software and you remove the
network cable, the current settings will stay active.
By switching from network control to local control you can easily switch between a configuration set using the Neumann.Control software and settings made directly on the subwoofer.
This can make sense if you want to temporarily use the subwoofer in a dierent location than
your measured studio environment.
The subwoofer does not lose its settings even when disconnecting it from the network or the
mains supply.
Resetting the KH 750 DSP
To reset the KH 750 DSP internal controls to their factory default values:
X
Switch on the KH 750 DSP.
X
While the power light is solid red during the boot up phase, move the AUTO STANDBY switch
G up and down repeatedly.
The power light will then flash red while the default settings are being applied before reverting to green.
Firmware update
Firmware updates are done via the Neumann.Contol software. When it is opened it surveys
the network for subwoofers and checks if the firmware is up to date. If a firmware update is
needed, you will be prompted to follow the on-screen instructions. It takes approximately 1.5
minutes per subwoofer to do the update.
KH 750 DSP | 17
Calibrating the subwoofer
Before using your system for the first time and whenever you change the physical conditions in
your listening environment, carry out the following steps:
X
Adjust the frequency response and the level of the loudspeakers before calibrating the subwoofer (see the operating manual of the loudspeakers):
Application Recommended frequency response Comments
Studio flat A flat response brings good
translation
Film X-curve shape ANSI/SMPTE 202M:
the shape of the X-curve
depends on the size of the room
Home subjective evaluation Not necessarily a flat response,
a gently downward sloping
response with increasing
frequency is often preferred
All the loudspeakers in the system should have the same level at the listening position. This
is often measured using a pink noise test signal that is set to -18 dBFS (Europe) or -20 dBFS
(USA) on the mixing console’s output level meters and a sound level meter set to “C-weighted”
and “slow”.
X
Calibrate the frequency response, the phase and the acoustical level of the subwoofer.
To do so, choose one of the following methods:
1. Alignment using Neumann.Control:
It is highly recommended to use Neumann.Control to calibrate the loudspeakers and
subwoofer in the room. Download the software and choose an Alignment method that
suits your circumstances: Precision, Guided, Manual.
2. Calibration using the backplate controls:
A: Calibration using an acoustical measurement system
Calibrating the frequency response, phase and sound pressure level by means of an
acoustical measurement system should always be your first choice since it yields the
highest accuracy. This method is described below.
B: Calibration using Neumann test signals
In the absence of an acoustical measurement system, you can calibrate the settings of
your subwoofer using Neumann test signals (see page 20).
C: Calibration using music signals and an 80 Hz test signal
A calibration by means of music signals is also possible but should always be the last
choice. In this case, play an 80 Hz test signal from your source equipment to calibrate
the phase (see page 20).
For setting up one or several subwoofers via Neumann.Control follow the on-screen
instructions.
KH 750 DSP | 18
Calibrating the
frequency
response
Calibration using the backplate controls and an acoustical measurement system
The settings of the switch SUBWOOFER GAIN | OUTPUT LEVEL A and the potentiometer
SUBWOOFER GAIN | INPUT GAIN B recommended in the following table are valid for
the following settings of your Neumann loudspeaker: INPUT GAIN: “0 dB” and OUTPUT
LEVEL: “100 dB SPL at 1m for 0 dBu”. For information on how to set your Neumann
loudspeaker, please refer to its operating manual. If the mentioned values cannot be set
on your loudspeaker, adjust the subwoofer accordingly.
The frequency response of a subwoofer depends on its position in the room and on the room
geometry. The same subwoofer installed in dierent positions in the same room may require
dierent acoustical control settings.
X
Adjust the frequency response of the subwoofer at your listening position. To do so, proceed
as follows:
X
Make sure that the switch SUBWOOFER GAIN | OUTPUT LEVEL A is set to “100 dB SPL at 1m
for 0 dBu”.
X
First, set the potentiometers SUBWOOFER GAIN | INPUT GAIN B and LOW CUT 5 to the
following settings. These settings can be used as a starting point for further adjustment:
Calibrating the
subwoofer level
Subwoofer position Setting of potentiometer
SUBWOOFER GAIN | INPUT GAIN B
Setting of potentiometer
LOW CUT 5
In a corner -8 dB 0 dB
Next to or flush
-4 dB 0 dB
mounted in an
acoustically solid
wall (e.g. brick,
concrete)
Next to or flush
-2 dB 0 dB
mounted in an
acoustically soft
wall (e.g. gypsum)
Free standing in an
-2 dB 0 dB
untreated room
Free standing in a
0 dB 0 dB
well-treated room
X
Check the frequency response at the listening position using your acoustical measurement
system:
• In the case of excessive very low frequency levels at the listening position, turn the
potentiometer LOW CUT 5 to the left. This reduces the output level of the subwoofer
towards lower frequencies.
X
Measure the subwoofer’s sound pressure level at the listening position.
X
Adjust the sound pressure level of the subwoofer so that the level of the frequency response
of the subwoofer below 80 Hz corresponds to the level of the frequency response of the
loudspeakers above 80 Hz.
• To do so, use the potentiometer SUBWOOFER GAIN | INPUT GAIN B and the switch
S UBWOOFER GAIN | OUTPUT LEVEL A. Make sure that the input signal is not too high.
Calibrating the
phase
X
Set the phase using the left switch SUBWOOFER PHASE D. Values from -180º to -315º can
be obtained by setting the right switch SUBWOOFER PHASE C to “–180º” and by adding the
set value of the left switch SUBWOOFER PHASE D.
Example: To obtain a phase shift of –270º, set the right switch SUBWOOFER PHASE C to
“–180º” and the left switch SUBWOOFER PHASE D to “–90º”.
X
Set the left switch SUBWOOFER PHASE D in combination with the right switch SUBWOOFER
PHASE C to values of 0
º
, -45º, -90º, -135º, -180º, -225º, -270º, and -315º, until you have
found the setting that gives the lowest sound pressure level at the listening position at the
cut-o frequency of 80 Hz (180º phase shift between subwoofer and loudspeaker, maximum
level cancelation).
KH 750 DSP | 19
X
Set the right switch SUBWOOFER PHASE C to the opposite position. The phase shift between
loudspeaker and subwoofer is now 0º. Check your subwoofer’s sound pressure level again
and, if necessary, readjust it so that it corresponds to the sound pressure level of the
l oudspeakers.
Your system is now completely acoustically calibrated.
Note that any change of the low cut influences the crossover phase. Therefore, the
phase and the level need to be recalibrated after changing the low cut EQ setting.
Calibration using the backplate controls and Neumann test signals
X
Download the Neumann test signals and the instructions for use (PDF file, in English) from
the KH 750 DSP product page at www.neumann.com.
X
Follow the steps described there.
Calibration using the backplate controls, music signals and an 80 Hz test signal
X
Adjust the settings for the sound pressure level and the frequency response as described
above.
X
Calibrate the acoustical phase using an 80 Hz test signal. Check the settings of the sound
pressure level and frequency response by means of music signals you are familiar with.
• Connect the left front loudspeaker to the socket OUTPUT | LEFT 8.
• Set the switch BASS MANAGEMENT E to “ACTIVE”.
• Play an 80 Hz test tone from your source into the audio input INPUT | LEFT 9 so that the
subwoofer and left loudspeaker are playing the tone.
• Set the left switch SUBWOOFER PHASE D in combination with the right switch SUB-
WOOFER PHASE C to values of 0
until you have found the setting that gives the lowest sound pressure level at the listening
position at the cut-o frequency of 80 Hz (180º phase shift between subwoofer and loudspeaker, maximum level cancelation).
• Switch o the test signal at the source.
• Set the right switch SUBWOOFER PHASE C to the opposite position.
The phase shift between loudspeaker and subwoofer is now 0
X
Check the settings of the sound pressure level and frequency response by means of music
signals. Listen for a smooth extension of the frequency response of the main loudspeakers
down to 20 Hz.
To to this, proceed as follows:
X
Listen to music containing content down to 20 Hz. Activate and disable the bass management
by repeatedly moving the switch BASS MANAGEMENTE between the two positions. There
should be no increase or decrease in level between the lower cut o frequency of the loudspeaker and 80 Hz.
º
, -45º, -90º, -135º, -180º, -225º, -270º, and -315º,
º
.
Compensating for larger time of flight (TOF) dierences
If the subwoofer is placed at a distance > 2 m (6'6") behind the loudspeakers with reference to
the listening position, the subwoofer back panel phase controls will not suce. In this case
use Neumann.Control to access the built-in delay functionality.
Using the bass management
X
For a two-channel stereo system set the switch CHANNEL B INPUT MODE J to “STEREO/
RIGHT”.
X
Set the switch BASS MANAGEMENT E to “ACTIVE”.
The bass management is activated. This inserts a 4th order 80 Hz high pass filter into the
signal path of the audio outputs OUTPUT | LEFT and RIGHT 8 and routes all audio signals
below 80 Hz to the subwoofer. The LED BASS MANAGEMENT F lights up green.
If you deactivate the bass management, the audio signal of the audio outputs OUTPUT | LEFT
and RIGHT 8 is only reproduced by the loudspeakers. Use this function to prevent the low
frequency signal components of the main channels being reproduced by the subwoofer.
X
Set the switch BASS MANAGEMENT E to “DISABLED”.
KH 750 DSP | 20
CHANNEL B INPUT MODE:
LFE-MODE 1
LFE-MODE 2
Remote-controlling the bass management
It is possible to activate and deactivate the bass management filters remotely using
Neumann.Control. This allows one to listen to the source as if there is no subwoofer connected
in the system because the loudspeakers play full range with no filtering when the bass management is disabled.
Setting the replay level of the subwoofer
This mode should be used when the signal has not been encoded already. Do not use this mode
when playing back DVDs, Blu-ray disks or if there is a bass manager before the subwoofer. The
LFE channel should be replayed at a level 10 dB higher than the main channels. The level can
be set in the monitoring matrix (console or external), or by setting an appropriate output level
on the subwoofer.
X
Connect the LFE channel to the socket INPUT | B 9 of the KH 750 DSP.
X
Set the switch CHANNEL B INPUT MODE J to “LFE MODE-1 or LFE MODE-2”.
X
Calibrate the frequency response of the subwoofer to be flat.
X
Measure the SPL of one of the main channels using pink noise and a sound level meter set to
“C-weighted” and “Slow”.
X
Measure the SPL of the LFE channel using pink noise and a sound level meter set to
“C-weighted” and “Slow”.
X
Adjust the level so it is 4 dB higher than the main channel. This corresponds to 10 dB more
(unweighted) level.
Note: As the level of the subwoofer aects both channels, do not connect a center channel to
the subwoofer when trying to add 10 dB to the LFE channel using the subwoofer level controls.
CHANNEL B INPUT MODE:
EXTERNAL BASS MANAGEMENT
CHANNEL B INPUT MODE:
LFE (FULLRANGE)
EXTERNAL BASS MANAGEMENT
The EXTERNAL BASS MANAGEMENT routing mode is used when there is a bass manager before
the KH 750 DSP subwoofer, e. g. an AV amplifier with activated bass management and loudspeakers set to “small”. It should also be used when a the LFE output of a DVD or Blu-ray player
is connected directly to the subwoofer (i.e. after the program material has been encoded). This
mode avoids double filtering of the bass managed signal but still allows the subwoofer’s frequency response to be calibrated.
X
In the source, set the bass management system to “On”.
This is typically achieved by setting the loudspeaker size to “Small”.
X
In the source, switch the subwoofer output to “On”.
X
In the source, choose a crossover frequency of 80 Hz.
X
In the source, select the crossover slope to be 24 dB/oct., if possible.
X
Connect the “Sub” channel to the socket INPUT | B 9 of the KH 750 DSP.
X
Set the switch CHANNEL B INPUT MODE J to EXTERNAL BASS MANAGEMENT.
X
Calibrate the frequency response of the subwoofer to be flat.
X
Set the level so it has the same level as the loudspeakers.
The LFE (FULLRANGE) routing mode is used when just the LFE signal of the source (DVD-player,
Blu-ray player or AV-amplifier) should be replayed by the subwoofer (i.e. after the program
material has been encoded). This mode avoids double filtering of the bass managed signal but
still allows the subwoofer’s frequency response to be calibrated.
X
In the source, set the LFE channel to “Sub out”.
This is typically achieved by setting the loudspeaker size to “Large” and “Subwoofer present”.
X
In the source, switch the subwoofer output to “On”.
X
Connect the “Sub” channel to the socket INPUT | B 9 of the KH 750 DSP.
X
Set the switch CHANNEL B INPUT MODE J to EXTERNAL BASS MANAGEMENT.
X
Calibrate the frequency response of the subwoofer to be flat.
X
Set the level so it has the same level as the loudspeakers.
KH 750 DSP | 21
Activating ground lift
If there is a humming or buzzing noise coming from the subwoofer, first search for the cause of
the noise:
X
Disconnect all input and output signal cables from the subwoofer.
If the noise goes away, it is probably coming from the audio source or source cabling. It might
be possible to eliminate the noise by disconnecting the ground from the input signals
(activating ground lift).
To activate ground lift:
X
Reconnect the signal cables and set the switch INPUT GROUND LIFT6 to “LIFTED”.
This internally disconnects pin 1 of all XLR input sockets from the subwoofer electronics’
chassis ground (see table on page 10).
For safety reasons, the electronics chassis ground is always connected to the mains
power earth pin. Never disconnect the earth pin of the mains cable from ground.
Even when ground lift is activated, the pin 1 of all audio inputs remain electronically
connected to each other.
Cleaning and maintaining the subwoofer
CAUTION
Damage to the product caused by liquids!
Liquids entering the product can cause a short-circuit in the electronics and damage or
even destroy the product.
X
Keep all liquids away from the product.
X
Before cleaning, disconnect the product from the mains power supply (see page 15).
X
Use a soft, dry, and lint-free cloth to clean the product.
KH 750 DSP | 22
Troubleshooting
Problem Cause Solution
There is hum or buzz coming
from the KH 750 DSP when an
analog audio cable is connected.
There is a sudden reduction of
the subwoofer’s output level,
the POWER ON LED H changes
from green to red, the output
level is reduced.
The POWER ON LED H lights
up red in time with low-frequency input signals.
The logo does not light up There is no LED behind the logo This normal. The logo does not
The back panel LEDs are o,
no sound is heard from the
KH 750 DSP.
A cable is defective, the cabling is
bad, there is ground loop in the installation or the level of the audio source
is too low.
The temperature of the power amplifier is too high.
The signal level is too high,
the protection system is active.
The KH 750 DSP main fuse has blown. Have the product checked by an
Check all cabling to eliminate the
cause of the problem, do not lay
signal cables parallel to mains
cables, use balanced cables, use
the ground lift switch (see page
22) or send higher signal levels
from your source and reduce the
level on your subwoofer and your
loudspeakers.
Ensure sucient ventilation of the
subwoofer and/or reduce the input
signal level, or add extra subwoofers to increase LF headroom. When
the temperature has dropped
again, the POWER ON LED H lights
up green and the output level
reduction is canceled.
Reduce the signal level.
light up.
authorized Neumann service
partner.
The KH 750 DSP is in standby Wake up the KH 750 DSP by play-
ing some audio into it.
The subwoofer sounds very
“thin” in the bass. The low
frequency response is very
low.
No signal is coming out of the
subwoofer and the connected
loudspeakers.
For further information, please refer to the “Questions & Answers” section at www.neumann.com.
Incorrect wiring in the analog audio
cable.
Both analog and digital signals are
connected.
Check the cabling, especially if
unbalanced cabling has been used
- see the cable wiring digram on
page 9.
If analog and digital sources are
connected simultaneously to the
subwoofer the digital source has
priority. As soon as a digital clock
signal is connected to the digital
input, this input is chosen by
default even if there is no audio
signal present. Remove the digital
connection if analog signal should
be replayed.
KH 750 DSP | 23
Specifications
For a complete list of the product specifications please refer to the product page of the KH 750 DSP at www.neumann.
com.
Product properties
Mains voltage 100 to 240 V ~,
50/60 Hz
Power consumption (idle / standby) 18 W / 0.3 W
Power consumption (full output AC) 410 W
Dimensions (H x W x D) 383 x 330 x 383 mm (15 1/8" x 13" x 15 1/8")
External volume 48.4 l
Weight 19.5 kg (43 lbs)
Driver 1 x 265 mm (1 x 10")
Cabinet surface finish, color painted wood (MDF),
metallic anthracite (RAL 7021),
painted back panel (RAL 9005)
Driver protection metal grille (RAL 9005)
Temperature
Operation and storage, unpacked +10 °C to +40 °C (+50 °F to +104 °F)
Transport and storage, packed in original packaging –25 °C to +70 °C (–13 °F to +158 °F)
Relative humidity
Operation and storage, unpacked max. 75 % (non-condensing)
Transport and storage, packed in original packaging max. 90 % (non-condensing)
Pin assignment of the XLR socket
1 Audio ground
2 Signal +
3 Signal −
Acoustical measurements and block diagram
Additional technical information such as acoustical measurements and a block diagram of the KH 750 DSP can be
found on the product page at www.neumann.com.
Mechanical drawings
Detailed mechanical drawings of all Neumann products are available at www.neumann.com.
Trademarks
Neumann® is a registered trademark of Georg Neumann GmbH. The following are trademarks of Georg Neumann
GmbH:
• Plane Wave Bass Array™ and PWBA™
• Neumann.Control™
Other company, product, or service names mentioned in this operating manual may be the trademarks, service marks,
or registered trademarks of their respective owners.
KH 750 DSP | 24
Technical information & glossary
Absolute
level
In Europe, the absolute level of 0 dBu is -18 dBFS (EBU standard R68). In the US, +4 dBu is -20 dBFS
(SMPTE standard RP155). These dBu values should lead to the following sound pressure levels:
Application Sound pressure level
Film 85 dB(C)
Broadcast 79 dB(C) (reference level)
Music No defined reference levels
Near field loudspeakers can be as close as 1 m from the listening position, whereas loudspeakers in
a Dolby certified movie mixing room should be at least 5 m from the listening position.
In the examples below, it is assumed that the listener is inside the room radius and thus the sound
field decays according to 20log
Absolute voltage level of input signal
Setting SUBWOOFER GAIN | INPUT GAIN B
SettingSUBWOOFER GAIN | OUTPUT LEVEL A
Listening distance [m] (dB change) 5 m (-14 dB) 5 m (-14 dB)
Measured output level in dB SPL at 1 m 85 dB SPL 85 dB SPL
Maximum input signal before activation
of the protection system
Absolute acoustic level calibration for signal channels is generally achieved using a sound level meter
set to “C-weighted” and “Slow”. Play a broadband pink noise test signal set to -18 dBFS (Europe) or
-20 dBFS (USA) on the console meters and measure the sound pressure level at the listening position. Then adjust each channel’s source level, not the loudspeakers and subwoofer(s) so that the
above stated sound pressure levels are achieved.
(r), however this may not always be the case.
10
0 dBu
(0.775 V)
-1 dB -5 dB
100 100
17 dBu 17 dBu
+4 dBu
(1.23 V)
Acoustical
axis
Acoustical
controls
The acoustical axis is a line perpendicular to the subwoofer’s front panel along which the microphone
was placed when tuning the subwoofer’s crossover during design. The acoustical axis is located at the
midpoint of the KH 750 DSP’s bass driver. Note that the subwoofer emits very low frequencies which
are emitted omnidirectionally. That is why the orientation of the subwoofer cabinet in the room does
not matter.
The backpanal acoustical controls are low-order DSP filters designed to compensate for some of the
acoustical issues commonly found in listening environments. The acoustical controls’ settings will
depend on the subwoofer’s location and will probably be dierent for the same subwoofer type positioned in dierent locations in the same room. When calibrating subwoofers there are three areas
requiring attention: in-room response, level relative to main loudspeakers, and phase relative to
main loudspeakers.
KH 750 DSP | 25
Acoustical
output level
Depending on the setting of the potentiometer SUBWOOFER GAIN | INPUT GAIN B and the switch
SUBWOOFER GAIN | OUTPUT LEVEL A — and referred to an input signal level of 0 dBu — the following
acoustical output levels can be obtained:
Setting of potentiometer
SUBWOOFER GAIN |
INPUT GAIN B
-12 dB 82 dB SPL 88 dB SPL 96 dB SPL 102 dB SPL
-10 dB 84 dB SPL 90 dB SPL 98 dB SPL 104 dB SPL
-8 dB 86 dB SPL 92 dB SPL 100 dB SPL 106 dB SPL
-6 dB 88 dB SPL 94 dB SPL 102 dB SPL 108 dB SPL
-4 dB 90 dB SPL 96 dB SPL 104 dB SPL 110 dB SPL
-2 dB 92 dB SPL 98 dB SPL 106 dB SPL 112 dB SPL
0 dB 94 dB SPL 100 dB SPL 108 dB SPL 114 dB SPL
+2 dB 96 dB SPL 102 dB SPL 110 dB SPL 116 dB SPL
The default setting is SUBWOOFER GAIN | INPUT GAIN B = “0 dB” and SUBWOOFER GAIN | OUTPUT
LEVEL A = “100 dB SPL at 1 m”, which corresponds to a sound pressure level of 100dB SPL measured at a distance of 1 m in free field conditions, when the input signal has a level of 0 dBu.
Using the potentiometer SUBWOOFER GAIN | INPUT GAIN B and the switch SUBWOOFER GAIN |
OUTPUT LEVEL A, you can compensate for level dierences due to acoustical loading (see page 8)
and due to dierent distances of the subwoofers and loudspeakers from the listening position.
Examples of how to calculate sound pressure levels as a function of the input signal levels and input
and output levels of the KH 750 DSP:
Absolute voltage level of
input signal
Setting SUBWOOFER GAIN |
INPUT GAIN B
SettingSUBWOOFER GAIN |
OUTPUT LEVEL A
Measured output level in dB
SPL at 1 m
Acoustic output level [dB SPL] of the subwoofer at 1 m
when input signal level is 0 dBu
Setting of switch SUBWOOFER GAIN | OUTPUT LEVEL A
94 dB 100 dB 108 dB 114 dB
0 dBu
(0.775 V)
0 0 0 0
100 100 100 100
100 104 106 116
+4 dBu
(1.23 V)
+6 dBu
(1.55 V)
+16 dBu
(4.89 V)
Acoustical
response
Neumann subwoofers are designed to have a flat pass band magnitude response in anechoic conditions when all the acoustical controls are set to 0 dB. When a subwoofer is installed into a listening
environment the response changes and thus should be corrected back to a flat response. It is therefore expected that the acoustical controls will need adjustment to improve the in-situ response of the
subwoofer. The acoustical controls’ settings depend on the subwoofer’s location and the dimensions
and behaviour of the room and will probably be dierent for the same subwoofer type installed in different locations in the same room. Moving the cabinet small distances, 50 cm (20"), can dramatically
change the response therefore resulting in dierent acoustical control settings.
Graphs of acoustical measurements conducted in anechoic conditions at a distance 1 m can be found
on the corresponding product pages at www.neumann.com.
KH 750 DSP | 26
Signal routing
For both analog and digital signals, the KH 750 DSP has two input and two output channels: LEFT / A
and RIGHT / B. After the electronically balanced or digital input stages, there are two 4th order 80 Hz
high pass filters for the main channels followed by two electronically balanced and digital output
stages. The signal connected to the left input is always routed to the subwoofer via a 4th order 80 Hz
low pass filter and to the left output via an 80 Hz 4th order high pass filter. This is the same for the
right input when the input mode is set to STEREO/RIGHT.
All outputs have protection circuits to avoid power on/o noises: the outputs switch on after a short
delay when mains power is applied and mute instantaneously when mains power is removed.
If you select the corresponding mode, there is also 120 Hz low pass filtering for an LFE channel, a full
range monitoring mode for routing the LFE channel content above 80 Hz to the A output, or a wide
input if you have an external bass manager (more details can be found on page Seite 20). Additionally a daisy chain mode allows you to connect additional subwoofers but this must be set up using
Neumann.Control.
th
Crossover Using 4
order filters, the crossover divides the input signal of each channel into two bands for reproduction by the subwoofer or the main loudspeakers. The crossover frequency is 80 Hz for the main
channels and can be bypassed when required. This default frequency was chosen to balance the conflicting requirements of having a high crossover frequency to relieve the main loudspeakers of their
low frequency duties thereby reducing distortion, and of the need to have a low crossover frequency
to minimize the chances of localizing the subwoofer thereby giving greater flexibility when placing
the subwoofer in the room. In addition, by choosing 80 Hz, there is a compatibility with the replay
conditions commonly found in consumer products. However, there are sometimes good reasons to use
a dierent crossover frequency so it can be changed using Neumann.Control.
Driver Long throw, ecient, low distortion driver ensures a clean sound quality even at high replay levels.
The driver is loaded by the internal volume of the cabinet.
LFE channel “Low Frequency Eects” (Dolby) or “Low Frequency Enhancement” (dts). The LFE channel has a lim-
ited bandwidth. Because of the limited frequency range of the LFE channel, it is referred to as “.1”
when describing, for example, a 5.1 system. The designation “LFE channel” always refers to the source
and not to the loudspeakers.
Power
amplifier
Protection
system
The high eciency power amplifier of the KH 750 DSP minimizes power dissipation and is run in
bridged mode to minimize distortion.
An extensive protection system prevents damage to the subwoofer if high signal levels are applied to
the input for a long time (the higher the signal the earlier the protection system is activated). The
POWER ON LED H changes from green to red when the protection system is active. In this case,
reduce the input signal level. If this happens regularly, use a larger subwoofer with a higher SPL output or add more subwoofers to the system to increase the LF headroom.
The protection system consists of thermal and peak limiters for the amplifier and thermal modeling of
the driver. The protection system is not a compressor, it is designed to protect the subwoofer from
damage. The protection system cannot protect against sustained abuse of the subwoofer system, i.e.
playing the subwoofer for long periods of time with the POWER ON LEDH lighted up red. Please
avoid consistent abuse of the subwoofer to not aect the long service life of the product.
KH 750 DSP | 27
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